Vacuum circuit breaker contacts consisting essentially of a copper matrix and solid solution particles of copper-tellurium and copper-selenium

ABSTRACT

A vacuum circuit breaker containing a pair of contact members relatively movable for contact or separation in which at least one of the contact members is made of an alloy consisting of copper matrix and solid solution particles of a Cu2Te - Cu2Se system dispersed in said copper matrix, the content of Se ranges between 0.1 and 5.0 percent, and that of Te ranges from 0.1 to 25.9 percent, their total content being 2.5 to 26 percent.

United States Patent [72] Inventors lsao Okutomi [52] US. Cl 200/144 B, Yokohama-sin; 200/166 C Klzuo Suzuki, Yokohama-shi; Hikohiro [5 l Int. Cl ..H0lh 33/66 Mizutani, Yokohama-5M; Kenichiro Ando, [50] Field of Search 200/ 144.2, Tokyo; Chiaki Hiruta, Yokohamashi; I66 C Akin Nabae, Tokyo; Tldahito Tsutsumi, Yokohamkshi n f Japan {56] References Cited [2! 1 Appl. No. 844,275 UNITED STATES PATENTS Filed J y 24, 1969 3,246,979 4/1966 Lafferty et al. 200/166 c x [45] Patented July 27, 1971 3,502,465 3/1970 Nakajima 200/144 B X [73] Assignee Tokyo Shihaura Electric Co., Ltd.

Kwmbshi, Japan Primary Examiner-Roben S. Macon 32 priority Ju|y 30 9 Attorney-Flynn & F rishauf J p [31] 43/53384 ABSTRACT: A vacuum circuit breaker containing a pair of contact members relatively movable for contact or separation in which at least one of the contact members is made of an [S4] VACUUM CIRCUIT BREAKER CONTACTS alloy consisting of copper matrix and solid solution particles of CONSISTING ESSENTIALLY OF A COPPER MATRIX AND SOLID SOLUTION PARTICLES 0F COPPER-TELLURIUM AND COPPER SELENIUM 2 Claims, 3 Drawing Figs.

a Cu Te Cu Se system dispersed in said copper matrix, the content of Se ranges between 0.1 and 5.0 percent, and that of Te ranges from 0.1 to 25.9 percent, their total content being 2.5 to 26 percent.

PATENTED JUL27 IH/i SHEET 1 OF 2 MAAA VACUUM CIRCUIT BREAKER CONTACTS CONSISTING ESSENTIALLY OF A COPPER MATRIX AND SOLID SOLUTION PARTICLES OF COPPER-TELLURIUM AND COPPER SELENIUM Background of the Invention The present invention relates to a vacuum circuit breaker and more particularly to a vacuum circuit breaker adapted to cut off large currents.

With a vacuum circuit breaker provided with a pair of contact members relatively movable for contact or separation, it is demanded that the contact members be possessed of good resistance to welding, circuit breaking property and static withstand voltage property and little subject to depletion, and also the chopping level be low. These properties are affected by the material of the contact member rather than by its geometric configuration.

As an approach to meet said requirements demanded of the contact member, there has been proposed an alloy prepared from a high conductivity metal such as copper and a metal admixed therewith, for example, bismuth or lead which has a low melting point and high vapor pressure and does not form substantially any solid solution in the first mentioned metal component. This known alloy has a structure in which the low melting metal is distributed along the grain boundary of the high conductivity metal. With said alloy, welding resistance is elevated by the bleeding to the surface of the low melting metal precipitated in the grain boundary of the high conductivity metal or the embrillted state of the boundary itself, and a desired circuit breaking property is obtained by changing the composition of said alloy, insofar as the welding resistance is not reduced. However, this alloy is not deemed fully satisfactory as the material of a contact member used in a vacuum circuit breaker which is increasingly demanded in recent years to have a large circuit breaking capacity. in other words, the prior art alloy has the drawbacks that where increased amounts of the low-melting metal are added in an attempt to elevate welding resistance, the circuit breaking property sharply drops, and that where the alloy consists of copper and bismuth, repeated interruptions of large currents cause copper crystals to be separated from each other and in consequence the copper particles to be prominently scattered off due to the relatively small binding force between the individual grain boundary, thus resulting in the depletion of the contact member and the decrease of its useful life. Another defect of the alloy is that the presence in an elemental form of the low melting metal in the area of copper particles prevents the contact member from displaying a fully satisfactory static breakdown voltage property.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide an improved vacuum circuit breaker, having a large circuit breaking capacity, provided with contact members which are little subject to depletion.

The contact member used in a vacuum circuit breaker according to the present invention is made of an alloy consisting of a copper matrix and solid solution particles of Cu Te-Cu se system dispersed in said copper matrix. The content of Se ranges between 0.1 to 5.0 percent, and that of Te ranges from 0.1 to 25.9 percent, their total content being 2.5 to 26 percent. Like a general particle dispersion hardened alloy, the alloy of the present invention has an increased hardness due to the presence of dispersed particles which are each composed of a Cu,TeCu Se system deemed as a pseudobinary solid solution material, and so displays a good breakdown voltage property. Further, the added tellurium and selenium do not assure an elemental form separately but are present in the form of a eutectic mixture deemed as a binary solid solution system as described above which has a relatively low vapor pressure. Accordingly, when the alloy of the present invention is used as the material of: contact member involved in a vacuum circuit breaker, it affords good welding resistance and circuit breaking property to the resultant contact member.

The present invention will be readily appreciated from the description taken by reference to the drawings.

The present invention will be readily appreciated from the description taken by reference to the drawings.

BRIEF EXPLANATION OF THE DRAWINGS FIG. l is a longitudinal sectional view of a vacuum circuit breaker of the present invention;

FIG. 2 is a ternary diagram showing the range of preferred proportions of the materials of a contact member used in a vacuum circuit breaker according to the present invention; and

FIG. 3 graphically shows changes in the electrical conductivity of the contact member with different amounts of additives in three kinds of alloys consisting of copper and said additives.

DETAILED DESCRIPTION OF THE INVENTION A preferred embodiment shown in H6. l of a vacuum circuit breaker according to the present invention includes a cylindrical outer shell 10 formed of suitable insulating material and a pair ofend plates l2 and 14 for closing up both ends of said shell 10. Between the end plates 12 and 14 and shell 10 are interposed packing members 16 and 18 to form an airtight chamber 20 defined by said shell 10 and end plates 12 and 14.

Through the central part of the upper end plate 12 extends inwardly a metal rod 22 coaxially with the shell 10. The metal rod 22 has a substantially disk-shaped contact member 24 secured at the end portion located within the shell 10, and is securely fixed on its surface contacting the upper end plate 12 by welding or other suitable means. The lower metal rod 28 penetrates a central hole 26 formed in the lower end plate 14 coaxially with the shell 10, and has a contact member 30 secured at the end portion positioned within the shell 10. Further, around the outer peripheral surface of that part of the lower metal rod 28 housed in the airtight chamber 20 is set up a substantially cylindrical metal shield 32. The shield 32 has a large diameter than the lower metal rod 28 and is disposed coaxially therewith. The end portion of the shield 32 close to the end plate 14 is open and the opposite end portion thereof is bent inwardly to be fixed on the outer peripheral surface of the lower metal rod 28. Between the bent end portion of the shield 32 and the inner surface of the lower end plate 14 is provided a bellows 34 in a manner to enclose the outer peripheral surface of the lower metal rod 28, thus enabling said metal rod 28 to reciprocate in the direction of its longitudinal axis with the chamber 20 kept in an airtight condition. The reciprocal motion of the metal rod 28 in the direction of its longitudinal axis allows the contact members 24 and 30 to be attached to and separated from each other. Such movement of the metal rod 28 is effected by a suitable driving mechanism (not shown) connected to that end portion of the metal rod 28 extending outside of the lower end plate 14. Numeral 36 denotes another substantially cylindrical shield coaxially disposed in the shell 10. One end portion of said shield 36 is fixed to the inner surface of the upper end plate 12 and the other end portion is opened at a point near the lower end plate 14. This shield 36 protects the inner surface of the shell 10 from the effect of metal vapors, while the first mentioned shield 32 saves the bellows 34 from such effect. Like an ordinary type, the present vacuum circuit breaker can be interposed between a power source and electrical circuit connected thereto by means of the upper and lower metal rods 22 and 28.

The interior of the airtight chamber 20 is evacuated at least to a degree of ID or preferably l0 to lo before the vacuum circuit breaker is finished.

At least one of the paired contact members involved in a vacuum circuit breaker of the present invention is made of the previously mentioned specific alloy, namely, a type consisting of a copper matrix and solid solution particles of a Cu Te-Cu Se system dispersed in said copper matrix. The content of tellurium ranges between 0.1 to 5.0 percent on the basis of the entire alloy and that of selenium ranges from 0.1 to 25.9 percent on the same basis, their total content being 2.5 to 26 percent.

Though the phase diagram of this alloy is not yet finally defined, the inventors research work shows that those areas where the total content of tellurium and selenium amounts up to 30 percent consist of a eutectic structure where there are precipitated in the copper matrix solid solution particles of an intermetallic compound having a composition of Cu TeCu Se. It is also microscopically confirmed that these particles are substantially spherical and homogeneously distributed in the copper matrix.

It is generally known that the circuit-interrupting property of a vacuum circuit breaker provided with contact members made of those types of alloy which are associated with the present invention remarkably varies with the content of a high vapor pressure metal in the alloy, the distribution pattern of said metal and the form in which it is present in the alloy. It may be generalized that the smaller the content of a high vapor pressure metal, the more improved will be the circuitinterrupting property of a contact member involved in a circuit breaker, though such contact member may be reduced in resistance to welding, and that based on the same alloy content, the circuit-interrupting property of the contact member will be more elevated when said high vapor pressure metal is present in a combined form than in an elemental form. This is due to the fact that a compound of said metal absorbs decomposition energy prior to evaporation and in consequence evolves under the same conditions smaller amounts of vapor than does its elemental form. This consideration obviously suggests that the alloy of the present invention advantageously elevates the currentnterrupting property of a contact member prepared therefrom. In this alloy, the added tellurium and selenium do not assume an elemental form but are present in the form of complicated intermetallic compounds which may be expressed by a chemical formula Cu Te-cu se. Accordingly, the alloy is extremely restricted in evolving its vapor under the conditions in which there will be placed the contact member of a vacuum circuit breaker. This means that the alloy allows a contact member prepared therefrom to display an excellent circuit-interrupting property.

As viewed from the circuit-interrupting property of a contact member, the maximum total content of tellurium and selenium is not subject to any particular limitation. However, the upper practical limit to said maximum content will be the level at which these metals tend to be segregated when an alloy containing them is melted. The inventors experiments show that if the total content of tellurium and selenium exceeds 26 percent on the basis of the entire alloy, then a contact member prepared from such alloy will sharply decrease in circuit-interrupting property. Further tests made on an allowable range for incorporating each of these metal additives indicate that there is obtained the good circuit-interrupting property of a contact member when the content of selenium ranges between 0.1 and 5 percent on the basis of the entire alloy and that of tellurium ranges from 0.1 to 25.9 percent on said basis. It is also confirmed that to allow a contact member to display a satisfactory resistance to welding, the minimum total content of tellurium and selenium should be 2.5 percent on the basis of the entire alloy. In brief, the alloy of the present invention contains 0.1 to 5.0 percent of selenium and OJ to 25.9 percent of tellurium. This alloy can be prepared by melting together the raw materials so mixed as to form a prescribed composition using a known process, for example, vacuum melting. Addition of a metal such as silver which has a greater electrical conductivity than copper will be effective to elevate the electrical conductivity of the resultant alloy.

There were conducted a series of tests to confirm the adaptability of the alloy of the present invention for use in the contact member of a vacuum circuit breaker. For these tests,

there were prepared contact members from the various alloys having compositions plotted on the ternary diagram of FIG. 2. The hatched region of said ternary diagram represents the allowable range of incorporating the raw materials for the alloy of the present invention. Each of the tested contact members had a diameter of 70 mm. The proportions of raw materials constituting the prescribed alloy compositions were vacuum melted by induction heating under a condition evacuated to 10 to 10 atm and cast into a specified mold. There were prepared two sample contact members for each type of alloy composition. Each group of two sample contact members was used in a vacuum circuit breaker as shown in FIG. I and tested for its circuit-interrupting ability. The test proved that the sample contact members consisting of an alloy prepared by the present invention succeeded at least three times in cutting offa current of 3.5 kv. and l3.I ka., whereas the contact members made of alloys whose composition was outside of the range of the present invention failed to interrupt said current.

There were carried out further tests to ascertain the depletion resistance of a contact member prepared from the alloy of the present invention. For this test, there was provided a contact member 70 mm. in diameter made of an alloy having a composition of Cu-tb 3.45 percent Te-O.77 percent Se and tested for its ability to cutoff a current of 7.2 kv. and 12 ka. in a state incorporated in a vacuum circuit breaker as shown in FIG. I. Tie number of circuit breaking cycles was counted until said contact member was depleted 3 mm. By way of comparison, there was tested under the same condition a contact member having the same dimensions and prepared from a known alloy having a composition of Cu-0.5 percent Bi. Similarly, the number of circuit breaking cycles was counted until said contact member was depleted 3 mm. As a result, it was disclosed that the contact member made of an alloy according to the present invention withstood 78 circuit breaking cycles, whereas the contact member consisting of the prior art alloy only withstood 45 cycles until the same degree of depletion was reached.

Moreover, the alloy of the present invention has another advantage that it has a far greater electrical conductivity than the known alloy containing a high vapor pressure metal. FIG. 3 presents changes in the electrical conductivity with increasing amounts of additives blended with the copper. Said conductivity is expressed in relative values to the electrical conductivity of pure copper. As apparent from FIG. 3, addition of tellurium and selenium only reduces the electrical conductivity of copper by about l3 percent. .This tendency does not noticeably change even when their total content exceeds 26 percent or the upper limit allowed for the composition of an alloy according to the present invention. In contrast, addition of, for example, 4 percent of lead decreases the electrical conductivity of copper as much as about 20 percent and further incorporation of lead linearly reduces said conductivity. Further, the electrical conductivity of an alloy containing 4 percent of bismuth Bi falls to about 60 percent of that of copper itself. The fact that the alloy of the present invention has such a high electrical conductivity means that where power is introduced through a contact member prepared therefrom, it presents a small heat buildup resulting from the Joule effect. This desirable property of the present alloy will prominently assist in elevating the welding resistance of the resultant contact member.

It will be apparent from the foregoing description that the vacuum circuit breaker of the present invention has a by far superior circuit-interrupting property and prominently longer useful life as compared with any known type. While it is preferred for said vacuum circuit breaker that a pair of contact members be all made of an alloy according to the present invention, a circuit breaker in which only one of the contact members is prepared from the present alloy even displays a better circuit breaking property than the prior art type. Ac cordingly, it will be understood that the present invention includes the last-mentioned type of vacuum circuit breaker.

We claim:

0.1 to 25.9 percent on the basis of the alloy, the total content of the selenium and tellurium being 2.5 to 26 percent on the basis of the alloy.

2. The vacuum circuit breaker according to claim I wherein said alloy contains silver. 

1. A vacuum circuit breaker having a pair of contact members relatively movable for contact and separation, where in at least one of the paired contact members is made of an alloy consisting essentially of a copper matrix and solid solution particles of a Cu2Te-Cu2Se system dispersed in said copper matrix, the content of selenium ranges between 0.1 and 5 percent on the basis of the alloy and that of tellurium ranges from 0.1 to 25.9 percent on the basis of the alloy, the total content of the selenium and tellurium being 2.5 to 26 percent on the basis of the alloy.
 2. The vacuum circuit breaker according to claim l wherein said alloy contains silver. 